Main objective of the study was to identify and document the ethno botanically important and economic plants of the Upper Subansiri district of Arunachal Pradesh, India. The Tagin, Hill Miri (now Nyshi) and Galo tribes of Upper Subansiri district of Arunachal Pradesh state of India use number of medicinal plants available in local forests as ‘traditional medicine’ for curing common illness. The ethnobotanical information was collected by field survey among aboriginal community, by study with herbaria and museum, by study of rituals, myths and folkfores and through folk market survey. The villages inhabited by the tribesmen were selected randomly for each tribe for the purpose of survey. The paper presents 140 numbers of medicinal plants used by these tribes for themselves and 18 numbers of plants for curing livestock diseases and for their feeding. Fresh leaves, young twigs, bark, fruits and roots are reported be used as traditional medicine for treatment of ailments among human beings and domestic livestock. The present documentation on the traditional medicine of the three tribes of Upper Subansiri district of Arunachal Pradesh emphasizes that many people of the region still depend upon herbal medicine for treatment of human as well as livestock diseases. Thorough biochemical investigation and clinical trials of local traditional medicines may provide new direction for human health care system. There is a need to focus on more ethnobotanical research, conservation and documentation of traditional medicinal knowledge among indigenous communities of the state.